Double acting linear electrical submersible pump and method for its operation

ABSTRACT

The invention relates to reciprocating piston pumps, in particular, to a reciprocating double acting well pump driven by a linear submersible permanent magnet motor. The essence of the claimed invention lies in the fact that the upper pumping plunger pair of a pump module of a double acting linear electric submersible pumping unit is configured to intake a double volume of a borehole fluid sufficient for one operating cycle and contains delivery traveling and inlet fixed valves with a directional pusher, closing by straight oncoming flow of the borehole fluid. Also a separator of downward and upward flows of the borehole fluid with low and high-pressure passages is installed above a cylinder of the pumping plunger pair. Wherein the low-pressure passages are performed in fluid communication with a borehole fluid delivery port from an annulus, containing a filtration and gravitational gas separation zone.

CROSS-REFERENCES TO RELATED APPLICATIONS

The present patent application claims priority to Ukrainian patent application a201800500 filed Jan. 17, 2018, Ukrainian Utility Model application u201800501 filed Jan. 18, 2018, Russian Utility Model application 2018110666 filed Mar. 26, 2018.

FIELD OF INVENTION

The invention relates to reciprocating piston pumps, in particular, to a reciprocating double acting well pump driven by a linear submersible permanent magnet motor.

BACKGROUND

General approach to recovered borehole fluid ascent to the surface includes utilization of a displacement pump driven by a mechanical drive.

There exists a distinction made for sucker-rod pumps, reciprocating of which is provided by a sucker-rod string. The sucker-rod pump unit consists of the displacement pump located at the bottom of an oil well tubing. The unit includes a piston moving linearly within the oil well tubing by means of steel or fiberglass rods. Linear movement of the pump rods is transmitted from the surface by means of a beam-type construction, designed to ascend and descend alternately the pump rods, thereby ensuring reciprocating movement of the pump piston.

The main disadvantage of this design is that most of wells are not straight and can deviate in different directions on their way to a production zone. Presence of deviations in a well direction causes friction between the pump rod and oil well tubing, which leads to their excessive wear and tear. Which results in high cost of structural elements replacement. In addition, presence of friction between the pump rod and oil well tubing requires utilization of motors of a higher efficiency.

An ordinary solving of this problem involves utilization of well pumps installed in the lower part of the oil well tubing. This kind of equipment includes downhole reciprocating double-acting pumps. A generic aspect of such pumps is that both strokes of a pump plunger are operational in order to maximize the efficiency of an electric motor during the reciprocating movement of the well pump. Major disadvantages of currently known pumping plants include significant losses of borehole fluid, malfunctions associated with presence of gas and mechanical impurities in the borehole fluid and restrictions regarding operability in wells with an inclination angle of more than 40°.

Claim for Invention US20150176574A1 dated Jun. 25, 2015, sets out a reciprocating downhole sucker-rod pump connected to a motor connector, for example, by a threaded or bolted flange couplings. The pump comprises an enclosure cylindrical and concentric on the axis. The pump includes an upper valve unit, comprising an upper intake port, and a lower valve unit; the cylinder is located concentrically between the upper valve unit and the lower valve unit within the pump enclosure. The upper valve unit is connected to the oil well tubing and has a pump outlet passage, that intercommunicates with an inner part of a pipeline. The enclosure and cylinder form a pump annular space between them. The pump piston or plunger interacts with the inner diameter of the cylinder providing ability of sliding. A crosshead beam is connected to the lower end of the plunger, causing reciprocating of the plunger with a moving part of the motor. Depending on the plunger stroke direction, the upper or the lower valve unit is activated, which provides supply of borehole fluid into a pump cylinder cavity, upon which it is brought to the surface by means of an annular channel in the oil well tubing.

Disadvantages of the described technical solution may include complexity of the design with arrangement of four valves and additional connecting-rod elements, which increases the installation dimensions and makes it complex to be manufactured.

Patent of Invention U.S. Pat. No. 6,817,409 dated Nov. 16, 2004, Int. Cl. F04B11/00, sets out a double-stroke piston pump installed in a borehole, driven by a linear drive, comprising an enclosure and a pumping plunger pair cylinder placed inside of it, with an annular cavity located in-between. The pump is capable to extrude the volume of the pumping plunger pair cylinder, by means of reciprocal motion of the plunger with a traveling valve connected to a moving part of the linear drive, providing that both strokes of the plunger are operational. According to the described design, the pump contains the plunger, traveling in reaction to the linear drive reciprocating. The pump is configured to supply the first volume of liquid to a well during an upward operational stroke of the pump and the second volume of fluid during a downward stroke. The pump piston is installed between the enclosure and the plunger so as to form an annular space between the plunger and the piston and an annular space between the enclosure and the piston. Also, the plunger design provides at least one through hole located between the piston and the lower portion of enclosure in order to create a fluid communication between a piston channel and the annular space arranged between the enclosure and the piston. Consequently, the fluid is being forced out from the annular space through at least one through hole of the plunger into the oil well tubing string during the plunger stroke.

Disadvantages of the described technical solution may include presence of a complex system of channels designed for fluid transmission, as well as a small volume of the borehole fluid supplied through the holes of the plunger. The disadvantages may also include the borehole fluid intake performed without gas withdrawal and filtration.

RU139596 Utility Model Patent dated Apr. 20, 2014, Int. Cl. F04B47/08, sets out a double-acting well pump driven by a linear drive containing a pump module with a reversing and inlet valves, as well as two successively mounted plunger pairs of different diameters, driven by the linear drive and capable to provide an ability to force the internal volume of the borehole fluid out by means of reciprocal motion of the linear drive. One of the plunger pairs is equipped with a traveling valve and forms an annular cavity with a pump module enclosure, providing that both plunger strokes are operational. The plunger pairs of the pump module are interconnected with a connecting rod. Diameter of the upper plunger cylinder is greater than diameter of the lower plunger cylinder. The upper plunger of a greater diameter is hollow and contains an installed discharge valve, the lower plunger of a smaller diameter is monolithic and connected by a polished rod with the working pump drive. The cavity located above the hollow plunger of a greater diameter is connected to a drill-string-borehole annulus through a suction valve. The cavity located under the monolithic plunger of a smaller diameter is permanently connected to the drill-string-borehole annulus. The cavity located under the upper hollow plunger of a greater diameter is connected to the cavity located above the lower monolithic plunger of a smaller diameter and with a bypass passage formed by a shell enclosing the upper larger cylinder from the outside; the bypass passage is connected to a pump flowout line.

Disadvantages of the described technical solution may include presence of harmful effect of gas and mechanical impurities contained in the borehole fluid due to filtration and gas separation non-availability, complexity of the construction due to a spaced-apart arrangement of the plunger pairs with a system of channels in valve units for fluid transmission, which can lead to their wax precipitation, also the pumping unit design does not allow its utilization in wells with an inclination angle of more than 40°.

The claimed invention aims solving a technical problem constituting creation of the double acting linear electric submersible pumping unit with increased productivity and simplified construction actuated by the linear drive in the form of a movable part (slider) of linear submersible permanent magnet motor, providing a possibility of raising the borehole fluid without no-load operation of the movable part and a possibility of operation in horizontal wells.

SUMMARY

The technical result achieved from the invention embodiment consists in simplifying of the construction with simultaneous increase in pumping unit productivity, reducing concentration of mechanical impurities of the borehole fluid and non-associated gas at a pump module suction, as well as in enhancement of the pumping unit operation in wells with an inclination angle of more than 40°, particularly in horizontal wells.

The essence of the claimed invention lies in a fact that the upper pumping plunger pair of the pump module of the double acting linear electric submersible pumping unit is configured to intake a double volume of borehole fluid sufficient for one operating cycle and contains the delivery traveling and inlet fixed spool valves, both with a directional neck, closing by straight oncoming flow of borehole fluid. Also a separator of downward and upward flows of the borehole fluid with low and high-pressure passages is installed above the cylinder of the pumping plunger pair. Wherein the low-pressure passages are performed in fluid communication with a borehole fluid delivery port from the annular space, containing filtration and gravitational gas separation zone. Volume of the gravitational gas separation zone is greater or equal to the volume of one operating cycle of the pump module. Wherein the plunger of the lower plunger pair is partially accommodated in the pumping plunger pair cavity while forming the annular cavity and is capable to execute labyrinth sealing of the linear drive movable part.

The annulus located between the pump module enclosure and the outer surface of the cylinder of the pumping plunger pair is connected to the annular cavity formed by the plunger of the lower plunger pair by means of a common volume arranged between the plunger pairs.

The borehole fluid filtration zone is arranged within the lower plunger pair; the borehole fluid periodically fills the cavity in the pump module enclosure formed by the difference in radial dimensions of the plunger and the linear drive connected to it.

A method of operation of the double acting linear electrical submersible pump comprises:

-   -   (a) lowering the pump module connected to the linear drive into         a well;     -   (b) filling it with the borehole fluid and displacing of the         borehole fluid subsequently into the tubing string cavity by         reciprocating of the plunger pair with the traveling valve,         connected to the movable part of the linear drive, wherein both         plunger strokes are operating;     -   (c) performing the borehole fluid intake from the annulus during         the downward stroke with open inlet and closed traveling valves         of the pumping plunger pair, simultaneously filling the double         volume of the cylinder of the pumping plunger pair required for         one operating cycle;     -   (d) pushing the borehole fluid through the filtration zone and         the gravity gas separation zone arranged in the borehole fluid         delivery port, provided that its volume is larger or equal to         the volume of one operating cycle of the pump module;     -   (e) displacing the borehole fluid from the annular cavity         located under the plunger of the pumping plunger pair         simultaneously during the downward stroke by means of its common         volume arranged between the plunger pairs and the annular cavity         connected therewith, located between the pump module enclosure         and the outer surface of the pumping plunger pair cylinder,         towards the high-pressure channels arranged within the separator         of the descending and ascending flows of the borehole fluid         installed above the pumping plunger pair cylinder, and further         through the reversing valve into the tubing string;     -   (f) inverting the borehole fluid flow on the reverse stroke,         namely upwards with closed inlet and open traveling valves of         the pumping plunger pair, under influence of a pressure created         within the cavity of pumping plunger pair cylinder towards the         common volume located between the plunger pairs;     -   (g) feeding it towards the tubing string by analogy with the         downward stroke, herewith the traveling, inlet and reversing         spool valves are closed by straight oncoming flow of the         borehole fluid.

BRIEF DESCRIPTION OF THE DRAWINGS

The essence of the claimed invention is explained, but is not limited to the following images:

FIG. 1 is a functional diagram of the pump module during the upward stroke;

FIG. 2 is a functional diagram of the pump module during the downward stroke.

FIG. 3 shows the valve of pumping module.

FIG. 4 shows the variant of pumping module valve.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIGS. 1, 2 show pump module 1 of the double acting linear electrical submersible pump installable into a wellbore and driven by means of the linear drive executed as movable part (slider) 2 of linear submersible permanent magnet electric motor (not shown on the illustration).

Pump module 1 contains enclosure 3 of a high pressure and of a cylindrical form with reversing 4 and inlet 5 valves; two plunger pairs 6, 7 are arranged on-line inside of the enclosure, driven by the linear drive capable to force out the internal volume of the borehole fluid due to the reciprocal motion of the linear drive. Upper pumping plunger pair 6 contains delivery traveling gravity or spool valve 8 and inlet fixed gravity or spool valve 4 installed in the upper portion of its cylinder, both with the directional pusher, and both of which are closed by the oncoming flow of the borehole fluid. Also the pumping plunger pair forms annular cavity 9 with the pump module enclosure. Stroke of the pump module plungers in both directions is operational.

Upper pumping plunger pair 6 with integrated traveling delivery 8 and fixed inlet 5 valves is connected to lower plunger pair 7 of a smaller diameter by means of its plunger. The mentioned plunger pair is also designed as the labyrinth sealing to prevent losses of the borehole fluid and protect the linear drive from abrasive wear due to mechanical impurities effect and allows to increase the plunger stroke of the pumping plunger pair with increasing the pump module productivity.

Lower plunger pair 7 is connected to linear drive 2, and its plunger 10 partially located inside of the cavity of cylinder 11 of upper pumping plunger pair 6 with forming annular cavity 12 under its plunger 13. Herewith annular cavity 12 is executed in fluid communication with annular cavity 9, arranged between the pump enclosure and outer surface of the pumping plunger pair cylinder by means of common volume 14, arranged between the plunger pairs. Flow separator 15 of downward 16 and upward 17 flows of the borehole fluid with low-pressure 18 and high-pressure 19 passages respectively is installed above the cylinder of pumping plunger pair 6. Wherein the low-pressure passage is executed in fluid communication with channel 20 of borehole fluid feed from the annulus, that includes zone 21 of filtration with arranged filters

And gravitational gas separation zone 22, volume of which is greater or equal to the volume of one operating cycle of pump module 1. The volume of one operating cycle is determined by the volume of fluid forced out during a single upward and downward stroke of plungers of the pumping module. Additional reversing valve 4 preventing a drain back of the borehole fluid from the oil well tubing is installed at an output of the pump module in a place of its connection to the oil well tubing string (not shown on the figures). Traveling 8, inlet 5 and reversing 4 valves are executed as valves with a directional pusher 25 and are capable to be closed instantaneously by straight oncoming flow of the borehole fluid, which provides reliable operation of the section isolation valves. Consequently, it is possible to significantly simplify the design of the pump module and avoid losses of the borehole fluid as against utilization of gravity valves, used in corresponding patents.

Borehole fluid filtration zone with filters 23 is arranged within the lower plunger pair for filtration of the borehole fluid, periodically filling cavity 24 in the pump module enclosure formed by the difference in radial dimensions of plunger 10 and linear drive 2 connected to it.

It should also be noted that the radial dimensions of plunger pairs 6 and 7 are assorted in a manner providing approximate equality of the liquid volumes pumped during upward and downward strokes.

According to said invention, traveling 8, inlet 5 and reversing 4 valves with directional pusher rod 25 which contacts with locking element 26 and closed by the straight oncoming flow of the borehole fluid.

Pump module valves (FIG.3) comprise cylindrical body 27 with locking element 26 inside of the cylindrical body, that is made in form of a ball. A motion of locking element 26 is enabled by means of hollow pusher rod 25 with a plurality of recirculation holes 28 crossing a body of the pusher rod with an angle to its central axis. Said embodiment providing that an area of increased hydraulic resistance is arranged within the pusher rod cavity 29, which creates a hydraulic pressure necessary for a translation movement of the pusher rod.

According to another variant of invention (FIG.4), pump module valves comprise a cylindrical body 30 with locking element inside of the cylindrical body, which made in form of directional neck 31 with sealing cone 32, closing by a straight oncoming flow of the borehole fluid, named locking element is made in solid-metal form and consists on parts with a variable radial cross section.

The locking element inside of the cylindrical body is made of materials with variable hardness. For example, locking element 26 is made of a material, hardness of which is greater than a hardness of pusher rod 25 in preferred variant of implementation (FIG. 3). In both said variants (FIG. 3,4), pusher rod 25 or directional neck 31 are made or covered with inert, corrosion-resistant and friction material.

The method for operation of the Double Acting Linear Electrical Submersible Pump utilizing the pump module of the described design involves lowering of the said pump module together with the installation into a well and filling it with the borehole fluid with its subsequent displacement into the oil well tubing string cavity by means of reciprocal motion of plunger pairs 6, 7 connected to movable part of linear drive 2, while both plunger strokes are operational.

The borehole fluid intake from the annulus is conducted during the downward stroke (FIG. 2), with pumping plunger pair inlet valve 5 open and traveling valve 8 closed, while filling the double volume of the cylinder of pumping plunger pair 6 that is sufficient for one operating cycle. Herewith the borehole fluid is being pushed through filtration zone with filters 21 installed and gravitational gas separation zone 22, arranged in the borehole fluid delivery port 20. A volume of gravitational gas separation zone 22 is executed to be greater or equal to the volume of one operating cycle of the pump module, which provides effective separation of gas particles from liquid particles and brings them out to the annulus, as shown in FIG. 2. Simultaneously, during the downward stroke the fluid is pushed out from annular cavity 12 under plunger 13 of upper pumping plunger pair 6 by means of common volume 14 arranged between the plunger pairs and annular cavity 9 connected to it, towards high-pressure channels 19, arranged within separator 15 of downward and upward flows of the borehole fluid and further through reversing valve 4 into the oil well tubing string. The flow separator is installed above cylinder 11 of upper pumping plunger pair 6. During the return upward stroke (FIG. 1) with pumping plunger pair inlet valve 5 closed and traveling valve 8 open, under the effect of pressure created in cylinder cavity 11, the borehole fluid flow is spread towards common volume 14 located between the plunger pairs and, from analogy of the downward stroke (FIG. 2), is fed towards the oil well tubing string.

Also during the upward and downward strokes constant circulation of the borehole fluid is performed within lower plunger pair 7 (as shown in FIG. 1.2) by means of periodical filling of cavity 24 located in the pump module enclosure formed by a difference in radial dimensions of plunger 10 and linear drive 2 connected to it. The borehole fluid filtration zone with set of filters 23 is arranged in order to provide protection of the linear drive from mechanical impurities.

An embodiment of the claimed invention contributes to achievement of the mentioned technical result by providing simplification of the design while increasing the productivity of the pumping unit utilization by using the set of valves with absence of a complex system of channels for borehole fluid passage, which allows to regulate the fluid motion within the pump module cavity without losses even with its horizontal positioning in a well. Also the arrangement of filtration and gravitational gas separation zones provides possibility of protection from harmful effect of gas and mechanical impurities, containing in the borehole fluid.

The claimed method provides various options and alternative forms of embodiment. A particular embodiment is disclosed in the description and illustrated by means of the given graphic materials. Described embodiment of the invention is not limited to a particular disclosed form and may encompass all possible embodiments, equivalents and alternatives, within the limits of essential features disclosed in the claim. 

1. A double acting linear electrical submersible pump, including: a pump module with reversing and inlet valves, as well as two successively mounted plunger pairs of different diameters driven by a linear drive 2 and configured to displace an internal volume of a borehole fluid by means of the linear drive reciprocal motion, one of which is equipped with a traveling valve 8 and forms an annular cavity 9 with a pump module enclosure, providing that both plunger strokes are operational, distinctive in that an upper pumping plunger pair 6 is configured to collect a double volume of the borehole fluid sufficient for one operating cycle and contains a delivery traveling and an inlet fixed valves, which are equipped with directional pusher rod 25, moving by a flow of the borehole fluid, also a separator 15 of a downward 16 and an upward 17 flows of the borehole fluid with low 18 and high 19 pressure channels is installed above a cylinder 11 of the upper pumping plunger pair 6, with low-pressure channels arranged in fluid communication with a delivery port 20 of the borehole fluid from an annular space, containing a filtration zone 21 and a gravitational gas separation zone 22, a volume of which is greater or equal to a volume of an operating cycle of the pump module, while a plunger 10 of lower plunger pair 7 partially placed into the upper pumping plunger pair cavity forming an annular cavity 12 and capable of a labyrinth sealing of a movable part of the linear drive.
 2. The double acting linear electrical submersible pump according to claim 1, wherein the annular cavity 9 between the pump module enclosure and an outer surface of the pumping plunger pair cylinder is connected with the annular cavity 12 formed with the plunger of the lower plunger pair by virtue of a common volume 14 arranged between the plunger pairs.
 3. The double acting linear electrical submersible pump according to claim 1, wherein a borehole fluid filtration zone 23 is arranged within the lower plunger pair 7, the borehole fluid which periodically fills a cavity 24 in the pump module enclosure formed by a difference in radial dimensions of the plunger 10 and the linear drive 2 connected to it.
 4. The double acting linear electrical submersible pump distinctive in that pump module valves comprise a cylindrical body 27 with a locking element 26 inside of the cylindrical body 27, motion of which is enabled by means of a hollow pusher rod 25 with a plurality of recirculation holes 28 crossing a body of the pusher rod with an angle to its central axis, providing that an area of increased hydraulic resistance is arranged within a pusher rod cavity 29, which creates a hydraulic pressure necessary for a translation movement of the pusher rod.
 5. The double acting linear electrical submersible pump according to claim 4, wherein pump module valves comprise the cylindrical body with the locking element inside of the cylindrical body, which is made in a form of a directional neck 31 with a sealing cone 32, closing by a straight oncoming flow of a borehole fluid, the above mentioned locking element is made in a solid-metal form and consists of parts with a variable radial cross section.
 6. The double acting linear electrical submersible pump according to claim 4, wherein the locking element arranged inside of cylindrical body 27 is made of a material, a hardness of which is greater than a hardness of the pusher rod
 25. 7. The double acting linear electrical submersible pump according to claim 4, wherein the pusher rod or the directional neck are made or covered with inert, corrosion-resistant and friction material.
 8. A method of operation of a double acting linear electrical submersible pump comprises: a) lowering a pump module connected to a linear drive into a well; b) filling it with a borehole fluid and displacing of the borehole fluid subsequently into a tubing string cavity by reciprocating of a plunger pair with a traveling valve, connected to a movable part of the linear drive, wherein both plunger strokes are operating; c) performing the borehole fluid intake from an annular space during a downward stroke with open inlet and closed traveling valves of an upper pumping plunger pair, simultaneously filling a double volume of a cylinder of the upper pumping plunger pair required for one operating cycle; d) pushing the borehole fluid through a filtration zone and a gravity gas separation zone arranged in a borehole fluid delivery port, provided that its volume is larger or equal to the volume of one operating cycle of the pump module; e) displacing the borehole fluid from an annular cavity 12 located under the plunger of the upper pumping plunger pair 6 simultaneously during the downward stroke by means of its common volume arranged between the plunger pairs and an annular cavity 9 connected therewith, located between a pump module enclosure 3 and an outer surface of a upper pumping plunger pair cylinder 11, towards high-pressure channels 17 arranged within a separator 15 of downward 16 and upward 17 flows of the borehole fluid installed above the upper pumping plunger pair cylinder 11, and further through a reversing valve 4 into a tubing string; f) inverting the borehole fluid flow on a reverse stroke, namely upwards with closed inlet 5 and open traveling 8 valves of the upper pumping plunger pair 6, under influence of a pressure created within the cavity 12 of the upper pumping plunger pair cylinder 11 towards the common volume 14 located between the plunger pairs; g) feeding borehole fluid towards the tubing string by analogy with the downward stroke, herewith the traveling 8, inlet 5 and reversing 4 valves are closed by the straight oncoming flow of the borehole fluid. 